Purpose:
To determine the influential factors for Infantile Nystagmus Syndrome (INS) patients' ability to acquire and pursue moving targets using predictions from the behavioral Ocular Motor System (OMS) model and data from INS patients.
Methods:
Eye-movement recordings used a high-speed digital video system. We studied five INS patients who pursued a 10 deg/sec ramp target to both left and right. We measured their target-acquisition times based on position criteria. The following parameters were studied: Lt (measured from the target-ramp initiation to the first on-target foveation period); target pursuit direction; and foveation-period pursuit gain. Analyses were performed in MATLAB environment using OMLAB software (OMtools, downloadable from http://www.omlab.org).
Results:
Ramp-target timing determined target acquisition time. The closer to the intrinsic saccades in the waveform the ramp stimuli started, the longer was Lt (Figure, upper and middle panels). However, arriving at the target position may not guarantee its foveation (Figure, lower panel). Pursuit gains vs. target direction had an idiosyncratic relationship for each patient.
Conclusions:
INS patients acquire ramp targets with longer latency for target initiations during or near the intrinsic saccades, consistent with the findings in our step-stimuli timing study. This effect might be due to the interaction between the saccadic and pursuit systems. Each INS subject had a directional preference in smooth pursuit gain. The combined effects of target timing and pursuit gain determined how fast and how well the INS subjects pursued ramp stimuli. Relevance to upland bird hunting will be discussed.Figure:Upper panel: ramp stimulus began during the slow phase. Middle panel: initiation during the intrinsic saccades. Lower panel: target acquisition of 550ms but low and variable smooth-pursuit gain.
Keywords: nystagmus • eye movements: saccades and pursuits • ocular motor control